The national parks in the American West include some of the country's most treasured places: the world's first national park, Yellowstone; the gorges of Grand Canyon; Yosemite's dramatic rock domes; and Mesa Verde's cliff dwellings. Now, however, the continued ability of western national parks to bring enjoyment to the American people is at risk from an unprecedented threat: global warming. A climate disrupted by human activities poses such sweeping threats to the scenery, natural and cultural resources, and wildlife of the West's national parks that it dwarfs all previous risks to these American treasures.

Many scientists think the American West will experience the effects of climate change sooner and more intensely than most other regions. The West is warming faster than the East, and that warming is already profoundly affecting the scarce snow and water of the West. In the arid and semi-arid West, the changes that have already occurred and the greater changes projected for the future would fundamentally disrupt ecosystems. The region's national parks, representing the best examples of the West's spectacular resources, are among the places where the changes in the natural environment will be most evident. As a result, a disrupted climate is the single greatest threat to ever face western national parks.

If we let climate change continue unchecked, the effects on scenery, natural resources, and wildlife in western national parks could include the following:

All the glaciers in Glacier National Park could melt away by 2030. Other national parks are also losing glaciers-including North Cascades National Park, which has 60 percent of the land covered by glaciers in the United States south of Alaska.

The dramatic snow-covered mountain peaks of Glacier, Grand Teton, Mount Ranier, North Cascades, Rocky Mountain, Yosemite, and other national parks could be barren of snow in the summers, when most people visit national parks.

Areas of treeless alpine tundra could be reduced or eliminated, including in Rocky Mountain National Park, home to the largest expanse of tundra in the United States south of Alaska.

Joshua trees could be eradicated from Joshua Tree National Park.

High temperatures and drought (both likely to increase further with climate change) are already combining to threaten the elimination of entire forests in the American Southwest, including in Bandelier National Monument and Mesa Verde National Park.

In national parks in mountain areas across the West, higher temperatures are likely to sharply reduce the presence of meadows and wildflowers.

The characteristic plant cover of many national parks across the West may change, with forests pushed upslope to mountain tops, one type of forest replacing another, and grasslands replacing forests. More invasive plant species are also likely to spread farther into western national parks, causing environmental and economic damage.

Unnatural increases in the frequency and severity of wildfires could imperil some natural resources, perhaps even threatening the existence of giant saguaro cacti in Saguaro National Park.

Wildlife species are likely to be pushed into extinction, either completely or locally in particular parks. Especially vulnerable are mountaintop species, including ptmarmigan (grouse-like birds), pikas (small alpine mammals), and desert bighorn sheep.

Climate change can have complex, cascading effects on natural resources in western national parks. For example, by ending the extreme cold that is the natural check on populations of mountain bark beetles, global warming is enabling them to infest whitebark pines, a high-altitude tree species previously out of their range. With no natural defenses to the beetles, whitebark pines could face extinction, robbing grizzly bears in and around Yellowstone National Park of one of their most important food sources and creating yet another hurdle to the long-term survival of the bears-the living symbol of the West's wildness.

A disrupted climate may also harm the cultural resources of western national parks by increasing flooding and erosion, wildfires, and sea levels, all of which can destroy historic buildings, historic and cultural landscapes, archaeological sites, and artifacts.

Climate change is also likely to interfere with the enjoyment Americans derive from western national parks. For example:

Unnatural increases in wildfires can disrupt summer vacations. A recent study concluded that since 1987 higher spring and summer temperatures and earlier snowmelt have contributed to a four-fold increase in western wildfires, with 6.5 times as much land being burned. With hot temperatures and earlier snowmelt likely to become even more common with global warming, additional increases in wildfire frequency and severity are likely. The greatest increases are projected for the northern Rocky Mountain region, putting Glacier, Yellowstone, and Grand Teton national parks at particular risk.

Beaches and other coastal areas of Golden Gate National Recreation Area, Channel Islands National Park, Point Reyes National Seashore, and Olympic National Park have been judged by the U.S. Geological Survey to be highly vulnerable to sea-level rise resulting from global warming.

Death Valley National Park, which already averages over 100 degrees Fahrenheit from late May through September, is likely to become intolerably hot for visitors for long stretches of the year. Other southwestern national parks are also at riskof becoming too hot.

Yosemite National Park and other relatively cool mountain parks are in danger of becoming overcrowded as a growing population in the West seeks to escape higher summer temperatures.

Reduced snowfall and snowpacks, earlier snowmelt, and increased drought may reduce opportunities for rafting, kayaking, and boating in western national parks, including Lake Mead and Glen Canyon national recreation areas. Also, reduced summer water flows and higher water temperatures are likely to greatly decrease the range and populations of trout and other coldwater fish in the West, reducing opportunities for recreational fishing in national parks.

With shorter and milder winters and less snow on the ground, Americans will have fewer opportunities to enjoy the magic of a snow-covered Yellowstone National Park or other western national parks.

Fortunately, these changes are not inevitable. There are many common-sense actions we can take now to reduce the worst future impacts of climate change. Encouragingly, more Americans are becoming aware of what is at stake, taking action themselves, and expecting action from their leaders. The National Park Service can do more to identify park resources and values that are at risk from a disrupted climate and take action to preserve them. The U.S. government must establish sensible standards that begin to significantly reduce our emissions of heat-trapping gases within 10 years if we are to avoid the most dangerous impacts caused by rising temperatures. In the face of inaction at the federal level, many states and cities are moving forward on their own, but much more can be done. Responsible and prudent action by all levels of government can make the difference in preserving not just the national parks of the American West but natural ecosystems and the quality of people's lives worldwide.

After fighting successfully for years to keep destructive logging, hydropower and mining projects out of their traditional territory, the people of Poplar River are now working to secure permanent protection for their boreal forest homeland.